A form of an information storage and retrieval device is a hard disk drive (hereinafter “disk drive”). A disk drive is conventionally used for information storage and retrieval with computers, data recorders, redundant arrays of independent disks (RAIDs), multi-media recorders, and the like. A disk drive comprises one or more disk media.
Each disk medium comprises a substrate upon which materials are deposited to provide a magnetically sensitive surface. In forming a disk medium, a substrate is ground or polished, conventionally by chemical-mechanical or mechanical polishing, to provide a substantially planar surface. Layers of materials are substantially uniformly deposited on the substantially planar surface to provide magnetic properties for writing to and reading from the disk media.
However, defects, such as pits, voids, particles, bumps, and scratches, among others, may arise on a disk medium surface. These defects affect the surface topography of the disk medium, and need to be detected and characterized. The characterization of disk surface topography is increasingly important due to the extreme reduction of head-to-media flying height spacing required to support ultra-high density digital magnetic recording. Research indicates that the disk micro-waviness, which is defined as topography in the wavelength range of 0.02 mm to 100 mm, has a substantial contribution to the head-disk separation margin, also known as disk contact (glide) avalanche. A model has been developed to predict glide avalanche of disk media from measurable properties of the media. A component of this model is HMS_Wq (r.m.s. Head-Media Spacing Modulation), which is calculated from the measurement of micro-waviness of the disk surface. To calculate HMS_Wq, the circumferential surface topography at a given radius on the disk is measured by use of high resolution surface profilometers, such as a Candela profilometer, quaduature phase shift interferometers (QPSI) or laser doppler vibrometers (LDV).
Measurement signals are provided to a processor that analyzes the spectrum of the surface topography by using Fast Fourier Transform (FFT). Integration of the product of the surface topography power spectral density (PSD) and an air bearing transfer function, evaluated over the micro-waviness wavelength range, determines the HMS_Wq. Taking an accurate and noise-free surface topography measurement is therefore a crucial step in the measurement of HMS_Wq. It has been observed that the measurement of the topography PSD spectrum is easily contaminated by noise sources, which may be electronic in origin or may originate from unwanted mechanical vibrations. Examples of such contaminating spectral components are shown in FIG. 1. It can be seen that these unwanted frequency components vary within the range of 1 kHz to 3 MHz. The existence of these noise sources in the surface topography PSD spectrum can severely affect the repeatability and reliability of the HMS_Wq measurements. A problem exists in that conventional filtering techniques cannot be applied because the noise is in the frequency band of interest.